In order to find publications regarding diet for MCI or dementia, the Web of Science Core Collection (WOSCC) was extensively searched. We employed a seasoned information retrieval expert with over 10 years of experience to oversee and review the development of our search terms. The data search strategy was “TI = Alzheimer* OR dement* OR “Frontotemporal Lobar Degeneration” OR “Lewy Bod*” OR “cognitive decline” OR “cognitive disorder*” OR “cognitive impairment” OR “cognitive dysfunction” AND TI = diet* OR food OR feeding OR nutrient* OR nutriment* OR nutrition AND Language = “English.” This study restricted publication types to “articles” and “reviews” and the search date is November 18, 2023 (Figure 1).

Downloaded from WOSCC, the data includes fully recorded and cited references. We used three analysis tools such as VOSviewer 1.6.17, CiteSpace 6.1.R3, and R language (version 4.3.0) bibliometrix package (version 4.1.2) for in-depth analysis. Key bibliometric measures include co-authorship, co-citation, and co-occurrence. Co-authorship analysis, for instance, focused on examining collaborative relationships among authors, nations, or institutions, as indicated by jointly authored papers. Analyzing co-occurrences is a quantitative approach to identifying relationships between components. Similarly, co-citation analysis was employed to evaluate the strength of connections between frequently cited elements. Thematic maps and three-field plots were drawn using Bibliometrix, an R package designed for bibliometric analysis.

VOSviewer, a software program for constructing and visualizing bibliometric networks, enabled us to analyze clustering patterns among nations, institutions, authors, and journals based on relationships such as co-authorship, common citations, or direct citations (22). Every node in the map that VOSviewer instantiates represents an element. By considering the quantity of publications, citations, and linkage potency of each component, VOSviewer made it easier to analyze clustering patterns among nations, institutions, authors, and journals. The number of nodes increases with the size of the node, and the number of links between nodes increases as the link width increases. CiteSpace was also a very useful tool for bibliometric analysis at the same time (23, 24).

Using CiteSpace, we analyzed keyword clustering and timelines, as well as the centrality of keywords. In CiteSpace, the following parameters were included: (1) each slice represents a year from 2003 to 2023; (2) single node type selection; (3) G-index based selection criteria, with k = 15; (4) using the pathfinder method, pruning was performed. Based on the Journal Citation Reports (JCR) 2022, the impact factor and category quartile data were calculated (25). Researchers, countries, journals, institutions, and journals are evaluated based on the H-index, a composite index of academic output.

We did not need Ethics Committee approval since all the data sources we used were publicly available.

The diet for MCI and dementia research literature contains 1,493 publications, of which 1,205 articles and 288 reviews account for 80.44 and 19.56%, respectively. Diets for MCI and dementia have been gaining a lot of attention since 2012. Three main phases are involved: (1) slow growth period (1980–2003): a slow and relatively flat growth in the number of annual articles, with the count remaining below 15; (2) stable increase period (2004–2017): in 2004, the annual number of publications exceeded 21 for the first time, and in 2014, 66 publications were published; (3) plateau period (2018–2023): over 100 publications were published annually, a significant increase (Figure 2).

The diet for MCI and dementia has been published in 82 countries since the turn of the century (Figure 3A). There are 42 countries with cumulative publications greater than five. Among all countries, the USA has published the most publications (557/37.3%), citations (32,950), and H-index (94), followed by China (239/16%) and the England (172/11.5%). USA works most closely with other countries (Figure 3B). In addition to Australia, Italy, and Japan, other countries are also showing a growing interest in research. A total of 2,134 institutions are involved in diet for MCI and dementia research (Figure 3C). With 38 cumulative publications and 5,328 citations, Columbia University is the first in the stratum. There are close academic ties, frequent academic interactions, and high-intensity collaborations in the Harvard Medical School, forming a global collaborative network. Figure 3D highlights the country’s collaboration with universities around the world in this field. The density of connections between university names, countries, and research topics gives us a glimpse of the USA leadership in these research fields, as well as the significant global influence and collaborative networks of institutions such as Harvard.

In total, 6,819 publications dealt with diet for MCI and dementia were published (Figure 4). Top ten authors are all high impact with H-index over 7 (Top ten authors are with H-index over 7), and Scarmeas Nikolaos, Morris Martha Clare, and Samieri Cecilia have 25, 19, and 17 publications, respectively (Table 1). Scarmeas Nikolaos has the highest H-index of over 20 and the highest average citation of 184.6. Martha Clare Morris has the greatest TLS and establishes a tight-knit group.

There were 521 publications related to diet for MCI and dementia, of which 60 journals had more than six publications (Figure 5). Journal of Alzheimer’s Disease topped the list of the 10 most productive journals with 76 publications and 2,911 citations. Followed by the Journal of Nutrients and Journal of Nutrition Health & Aging, with 75 and 42 relevant publications. It is Alzheimer’s & Dementia that has the most impact factor (IF) in the top 10 journals, which confirms their excellent level (Table 2). According to the H-index, Journal of Alzheimer’s disease (26) and Journal of Nutrition Health & Aging (27) have had a profound impact on the development of the field.

The publications yielded 432 keywords, 129 of which appeared more than 10 times (Figure 6A). AD, the name of the disease, ranked highest in frequency (734 occurrences) and association with other keywords. In addition, the top five frequency keywords also include dementia, Mediterranean diet, risk, oxidative stress. The top three centrality are apolipoprotein E, care, amyloid beta (Table 3). Using clustering analysis of keywords, we found 16 cross-over clusters, mostly related to disease name and classification (#1, #4, #6, #7), dietary patterns and specific nutritional patterns (#5, #9, #11, #0), Physiological factors and health status (#2, #3, #8, #10, #13), quality of life and health consequences (#12, #14, #15) (Figure 6B). Timeline plots were used to display temporal trends (Figure 6C). In the field of diet for MCI and dementia, “#1 mild cognitive impairment,” “#2 obesity,” “#3 insulin resistance,” “#4 cognitive function,” “#5 dietary pattern,” “#8 oxidative stress,” “#9 Ketogenic diet (KD),” “#10 amyloid beta” and “#13 weight loss” emerge as recent research frontiers.

Using CiteSpace software, the top 25 keywords on diet for MCI and dementia are analyzed to determine the hotspots and research trends (Figure 7). This timeline analysis of burst keywords specific to diet and dementia reveals a chronological progression of research focus areas. Initial bursts of keywords like “care” (1991–2008), “nursing home residents” (2001–2011), and “survival” (2001–2015), highlight an early emphasis on the practical aspects of care and longevity in dementia patients. Furthermore, the prominence of “percutaneous endoscopic gastrostomy” (2001–2011) underscores a period where nutritional interventions via medical procedures were a key area of investigation. “Ketogenic diet” has gained popularity, as well as “expression” and “gut microbiota.” Diet research for MCI and dementia is currently garnering attention, and indicates potential developments in the field.

We extracted 33,350 references, of which 872 were cited more than 10 times (Figure 8A). The top 10 cited references are mainly articles, focusing on the correlation between dietary patterns and dementia diseases. These important studies have been predominantly published in journals of significant influence, such as Lancet Neurol, Lancet, and Alzheimer’s Dement (Table 4). The most frequently cited reference is a review, which published in the Lancet Neurol written by Scarmeas N. harvested 62 citations. The paper by Livingston G. et al. was ranked second with 55 citations and there were 49 citations for the paper by Morris M. C. et al. Three of the most cited key papers emphasize the significant impact dietary and lifestyle interventions can have on reducing cognitive impairment, dementia, and AD (11, 28, 29). These studies reveal that specific nutrients and diets, notably the MIND diet, are associated with a marked decrease in AD incidence, emphasizing the role of modifiable factors such as nutrition, education, and lifestyle changes in dementia prevention (see Table 5).

A clustering analysis of references reveals that most of the references relate to dietary patterns and specific nutrients (#0, #1, #4, #5, #6#14), cognitive impairment is associated with disease (#3, #7, #9, #15, #19), feeding methods and related challenges (#2, #10, #11, #12, #13, #17), research data resources (#8, #16) (Figures 8B,C). Meanwhile, the burst analysis displayed the top 25 references (Figure 9). The five latest bursts and continuously emerging references emphasis the importance of diet in the research of cognitive impairment and dementia, particularly AD. These studies collectively highlight significant insights into the gut-brain axis, the effectiveness of specific dietary patterns like the MIND diet in reducing AD incidence, and the broader impact of nutrition on cognitive health. They reveal key associations between gut microbiota diversity, dietary patterns, and cognitive outcomes, advocating for a multifaceted approach in understanding and managing cognitive disorders. Although diet has a potentially positive impact on cognitive health in older adults, more research is needed to confirm it (29–33).

From the Figure 10, we can identify different categories of research topics in the fields of diet, cognitive impairment, and dementia. The figure shows “Alzheimer’s-disease” and “dementia” as the basic themes, which occupy a central position in the field of research, showing their status as core research topics. In addition, the placement of topics such as “Oxidative Stress,” “Brain” and “Mild Cognitive Impairment” indicates that they are currently actively developing research areas, reflecting the dynamics and trends of current scientific research. These developing topics indicate new research opportunities, as well as possible future research directions. Conversely, topics in the upper left and lower left quadrants may indicate a declining research interest.

Using the WoSCC databases, we searched for articles published about diet and MCI in the present study. The bibliometric study consisted of 1,493 papers from 2,134 institutions in 82 countries and regions with 6,819 authors, published in 521 journals with 33,350 co-cited references. Research on diet for MCI and dementia has experienced a slow growth period (1980–2003), a stable increase period (2004–2017), and may now be at an academic plateau. Recent years have seen an increase in the amount of scientific research produced on diet for MCI and dementia.

Cognitive impairment is a broad term that usually refers to a slight decline in memory, thinking, and judgment. MCI was first proposed by a team from New York University in the 80s of the 19th century as a form of cognitive impairment and is often seen as the primary stage of cognitive decline (37). On beginning of MCI, memory and cognitive abilities may decline further and may progress to more severe dementia. Dementia is an umbrella term that encompasses a variety of conditions with severe cognitive decline, the most common of which is AD, which is characterized by memory loss and loss of thinking and language skills (38). There are other types of dementia, such as vascular dementia, dementia with Lewy bodies, and dementia in the frontotemporal lobe, each with different causes and manifestations (39). It is important to note that not all people with mild cognitive impairment will develop dementia. Diagnosis and early intervention are important to manage and improve these conditions.

When exploring the management of cognitive impairment and dementia, it is particularly noteworthy that the KD, a dietary style that has attracted a lot of attention in cognitive impairment research in recent years. The KD, which refers to a high-fat, low-carbohydrate diet, has attracted a lot of attention in recent years in the study of cognitive impairment (40, 41). This eating pattern is designed to guide the body into ketosis, allowing the brain to use ketones instead of glucose as the primary energy source. This may be important for people with cognitive impairment, especially AD, who often have impaired ability to metabolize glucose in the brain. However, the strictness of the KD and the potential risk of nutritional imbalance are also factors to consider (42). Other dietary patterns are currently being studied in the MIND diet, DASH diet, and Mediterranean diet, which mainly protect the brain from inflammation and oxidative damage and reduce the risk of cognitive impairment by advocating more fruits, reducing the intake of fried foods, and improving the body’s antioxidant and anti-inflammatory properties (16, 27, 41). In addition to exploring different dietary patterns, such as the KD, the study also focused on dietary solutions for patients who were unable to eat on their own due to cognitive decline. In this case, tube feeding and percutaneous endoscopic gastrostomy (PEG) are important options to consider. Tube feeding refers to the intubation of the stomach through the nose, and PEG refers to the entry of the stomach through a small incision in the abdomen (26). Patients with dementia often have difficulty eating and drinking, and for people with dementia who are unable to eat on their own, tube feeding or PEG can provide essential nutrients (43). However, tube feeding has side effects such as aspiration, gastric retention, and the risk of accidental extubation, while PEG can be painful and may cause other adverse effects (pneumonia, poor bowel or bladder control, and bleeding, swelling, and infection), and its use is accompanied by ethical and clinical management challenges (26).

In recent years, studies have found that obesity, insulin resistance, oxidative stress, amyloid beta, and weight changes play an important role in cognitive decline. Chronic inflammatory states and metabolic disorders due to obesity can negatively impact brain health, including affecting cognitive function and promoting the development of neurodegenerative diseases (44). At the same time, obesity is associated with an increased risk of cardiovascular disease, which is also considered to be an important factor affecting cognitive impairment (45). In the brain, insulin not only regulates blood sugar levels, but is also involved in neuronal growth, survival, and synaptic function. Insulin resistance can cause neuronal damage and reduce synaptic plasticity, which can affect memory and learning ability (46). Moreover, insulin resistance is associated with abnormal accumulation of AD biomarkers such as amyloid beta and tau protein (47). Amyloid beta is the main component of age plaques in AD (48). Numerous studies have shown that the accumulation of amyloid beta is thought to be a key process leading to nerve cell damage and death, thereby affecting cognitive function. Accumulation in both nerve cells and outside of nerve cells can cause toxic reactions, leading to neuronal degeneration and death (48, 49). Clearance of neurotoxic amyloid beta in the brain is the primary strategy for remission and treatment of AD (50). Oxidative stress is a state of cellular damage caused by excessive production of free radicals, which plays an important role in the pathogenesis of cognitive impairment such as AD, especially related to the abnormal deposition of amyloid beta (51).

A large number of studies have focused on genetic factors closely related to MCI or AD, especially the gene polymorphisms of apolipoprotein E (ApoE). In addition to its function as a polymorphic protein, ApoE genes can be involved in many biological processes, which may contribute to the pathogenesis of dementia, particularly AD (52). ApoE has three gene variants, ε2, ε3, and ε4. In 1997, Farrer L. A. found that the frequency of ε4 increased in patients with late-onset familial AD. Subsequently, 46.2% of AD patients were found to carry the ε4 allele, while 13.2% of the control group were carried. In 2002, Zubenko et al. (53) reported that centenarians generally carry the ε2 gene. This discovery is a big step forward for ApoE polymorphisms and research. The relationship between ApoE polymorphisms and AD has been mainly focused on brain metabolism related to amyloid beta or tau protein, as well as neuronal growth and branching. Research on ApoE and its gene polymorphisms has become a hot topic in medicine. Considering the role of ApoE in the metabolism of lipoproteins, adjusting the type and amount of fat in the diet may be particularly important for ε4 carriers. At the same time, studies have found that nursing has been paid more and more attention in recent years in the direction of dietary intervention for MCI and dementia, and has achieved certain results (52, 54, 55).

The top three most cited key papers highlight the importance of diet in preventing cognitive impairment and dementia, especially AD. The study by Nikolaos Scarmeas published in 2018 highlighted nutrition as a lifestyle intervention that can alter cognitive decline risks (11). Despite the limited evidence, the study notes there is a protective association between certain nutrients (e.g., folate, flavonoids, vitamin D, and certain lipids) or food groups (e.g., seafood, vegetables, and fruits, and potentially moderate alcohol and caffeine consumption) and cognitive outcomes among older adults. Moreover, According to Livingston’s et al. (16) article, the incidence of dementia has fallen in many countries due to improvements in education, nutrition, health care, and lifestyle changes. Together the 12 modifiable risk factors (smoking, obesity, depression and et al.) as a result, around 40% of dementia cases worldwide may be prevented or delayed. In low-and middle-income countries where dementia occurs more frequently, prevention potential is higher. Morris MC, et al. published an article titled MIND diet associated with reduced incidence of AD in 2015 (29). The study found that the MIND diet was associated with a significant reduction in the risk of AD, with lower prevalence with higher adherence, with a 53% reduction in incidence in the group with the highest adherence, and even moderate adherence to the MIND diet may have significant benefits in preventing AD. The three studies focused on the role of diet in preventing cognitive impairment and dementia, highlighting the association of specific nutrients and healthy eating patterns such as the MIND diet with a reduced risk of AD. The study also identified several modifiable risk factors, including education, lifestyle, and environmental factors.

Three new trends in diet for MCI and dementia research were identified by analyzing keyword references with citation bursts. These are:

The Ketogenic diet (KD): first proposed by Can Med Assoc J in 1931 for managing epilepsy, particularly in children with refractory seizures, has since expanded its therapeutic potential to include the treatment of neurodegenerative diseases like AD (56). Recent studies suggest that the KD, by upregulating circulating β-hydroxybutyrate and altering gut microbiome composition and neurovascular functions, offers neuroprotective effects (57). These benefits stem from its ability to reduce oxidative stress at the mitochondrial level through ketone and polyunsaturated fatty acid (PUFA) production. Oxidative stress may also be a future research direction for the prevention and treatment of cognitive impairment (58). Additionally, evidence indicates the KD’s efficacy in reducing midlife mortality rates and improving memory in mice.

Expression: since 2016, there is a significant peak in citations of the keyword “expression,” indicating a growing scientific interest in gene or protein expression patterns related diet, cognitive impairment, and the development of dementia symptoms. Key focus areas included the interaction between diet and gene expression, especially antioxidants and omega-3 fatty acids have been found to influence cognitive health by regulating gene expression (59). The ε4 allele in the APoE gene is an important genetic marker for AD risk, and research focuses on how this gene interacts with dietary factors and influences the development of cognitive impairment (55). In addition, epigenetic studies revealed how environmental factors, especially diet, alter gene expression through mechanisms such as DNA methylation and histone modifications, which in turn influence the development of neurodegenerative diseases (60). Protein expression changes are also crucial in cognitive impairment development, with dietary factors affecting the expression of proteins associated with AD (61). Furthermore, “expression” is not only reflected in the expression of genes and proteins at the biological level, but also involves the expression of patients’ emotions and thoughts (62).

Gut microbiota: recent neuroscience research has focused on the interaction between gut microbiota and brain function, or the “gut-brain axis.” Intestinal flora plays a variety of roles in the occurrence and development of AD, according to recent studies. Thus, intestinal flora modulation is now considered a new treatment option for AD (63). By affecting the nervous, endocrine, metabolic, and immune systems, the intestinal flora affects AD occurrence primarily (64). AD has recently been treated and prevented by regulating intestinal flora (65). A study found that AD-associated intestinal flora (characterized by Bacteroidetes) enrichment could enhance microglial cell activation and neuroinflammation by activating the C/EBPβ/AEP pathway and upregulating pro-inflammatory PUFA metabolism by activating the C/EBPβ/AEP pathway, thereby promoting microglial cell activation and neuroinflammation, thereby promoting AD pathology and cognitive impairment. AD patients had different intestinal flora than healthy volunteers and patients with MCI (66).

Emerging analysis highlighted five key papers as the latest hotspots in the research on diet for cognitive impairment/dementia. Nicholas’s M. study unearthed significant differences in the gut microbiome of AD patients, notably a decrease in microbial diversity and distinct variations from age-and sex-matched controls, including diminished Firmicutes and elevated Bacteroidetes. This study also discovered correlations between various microbial genera and AD biomarkers in cerebrospinal fluid, suggesting a possible link for therapeutic intervention (33). In addition to the exploration of the gut-brain axis, another significant stride in this field is Martha’s C. M. research on the MIND diet, which has shown promising results in reducing AD incidence. Over a 4.5 year period, the study followed 923 participants aged 58–98, demonstrated the effectiveness of the MIND diet in lowering the rates of AD. Compared with DASH and Mediterranean diets, higher adherence to the MIND diet significantly reduced AD rates (29). Similarly, Diane’s E. Australian longitudinal study reinforced the MIND diet’s effectiveness, showing a reduced 12-year incidence of cognitive impairment, contrasting with the Mediterranean diet, which did not exhibit the same level of effectiveness (30). Scarmea’s et al. (31) research delved into the broader spectrum of nutrition and its preventive role against cognitive impairment, highlighting a protective association between certain nutrients and dietary patterns, especially the Mediterranean diet, and cognitive outcomes in the elderly. Lastly, Vincenzo’s systematic review synthesized recent observational studies, revealing a direct relationship between dietary patterns and brain structure/activity changes. It highlighted the synergistic health effects of dietary patterns like the Mediterranean, DASH, and MIND diets in reducing cognitive decline and AD rates (32). These comprehensive studies collectively underscore the critical role of diet in cognitive health, ranging from microbial interactions to dietary patterns, and advocate for a multifaceted approach to managing and understanding cognitive disorders.

In comparison to traditional reviews, bibliometric-based analyses provide a broader perspective on research priorities and trends in diet for MCI and dementia.

But the research has its limitations. Firstly, due to the continuous updating of WoSCC, the retrieval results of this study may not reflect the most recent literature. Secondly, no other databases were searched, such as Google Scholar or PubMed. Thirdly, this analysis might be less credible if the literature collected is of uneven quality. Lastly, only English literature is included, and some important non-English publications may be excluded, leading to the neglect of non-English papers.

Furthermore, the inherent challenges of dietary pattern research, particularly in relation to MCI and dementia, due to a myriad of confounding factors, compound the difficulty in drawing definitive conclusions. This complexity is exacerbated in a bibliometric context, where the reliance on secondary literature analysis navigates compounded uncertainties and may not fully capture the nuanced effects of dietary factors on cognitive health. The quality and biases inherent in the existing literature, including a possible publication bias towards positive findings, further limit the conclusions drawn from our analysis. By addressing these limitations, our aim is to present a comprehensive, transparent account of our study’s scope and the potential impacts of our findings, thereby not only enhancing the credibility of our research but also pointing to areas for future methodological refinement and investigation.